avoid using array variable

Author: baggepinnen

src/Blocks/math.jl

@@ -24,11 +24,11 @@ end
 Gain.f(k; name) = Gain.f(; k, name)
 
 """
-    MatrixGain(K::AbstractArray; name)
+    MatrixGain(; K::AbstractArray, name)
 
 Output the product of a gain matrix with the input signal vector.
 
-# Parameters:
+# Structural parameters:
 
   - `K`: Matrix gain
 
@@ -38,19 +38,19 @@ Output the product of a gain matrix with the input signal vector.
   - `output`
 """
 @mtkmodel MatrixGain begin
-    @parameters begin
-        K, [description = "Matrix gain"]
+    @structural_parameters begin
+        K
     end
     begin
-        nout = size(getdefault(K), 1)
-        nin = size(getdefault(K), 2)
+        nout = size(K, 1)
+        nin = size(K, 2)
     end
     @components begin
         input = RealInput(; nin = nin)
         output = RealOutput(; nout = nout)
     end
     @equations begin
-        [output.u[i] ~ sum(getdefault(K)[i, j] * input.u[j] for j in 1:nin)
+        [output.u[i] ~ sum(K[i, j] * input.u[j] for j in 1:nin)
          for i in 1:nout]...
     end
 end